Prefabricated buildings

ABSTRACT

A PREFABRICATED BUILDING UNIT, FOR FORMING THE STRUCTURAL FRAMEWORK OR BACK-BONE OF A TRANSPORTABLE PREFABRICATED BUILDING UNIT, CONSISTS OF A PREFABRICATED RECTANGULAR FLOOR PANEL STRUCTURE HAVING A PREFABRICATED VERTICAL LOAD-BEARING COLUMN RIGIDLY ATTACHED TO IT AT EACH CORNER AND AT AN INTERMEDIATE REGION IN THE LENGTH OF EACH SIDE. IN A MODIFICATION A COLUMN MAY BE OMITTED AT ONE CORNER, AND/OR FROM ONE SIDE, AND REPLACED BY A TEMPORARY COLUMN. ROOM ELEMENTS MAY THEREFORE BE CONSTRUCTED OF A LENGTH HITHERTO IMPRACTICABLE BECAUSE IN SITU, THE ROOM ELEMENTS IN EACH UPPER STOREY ARE SUPPORTED AT THE INTERMEDICATE REGION BY THE INTERMEDIATE COLUMNS OF THE LOWER ROOM ELEMENTS, THEREBY REDUCING THE UNSUPPORTED FLOOR SPAN. THE FLOOR PANEL STRUCTURE MAY BE A SINGLE PANEL OR TWO CO-PLANAR PANELS DISPOSED END TO END AT THE INTERMEDIATE REGION. IT MAY BE STRESSED TO PREVENT IT SAGGING (DURING TRANSPORT AND ERECTION OF THE ROOM ELEMENT) AT THE INTERMEDIATE REGION, THE STRESS MAY BE RELIEVED OR REDUCED AFTER THE ROOM ELEMENT HAS BEEN PLACED IN SITU.

March 9 'F. c. STUCKY 3,56 ,380

PREFABRI CATED BU ILDING S Filed Nov. 5, 1968 '7 Sheets-Sheet 1 INVli/V'IUR.

FRITZ CHRISTOPH STUCKY BY Bi 1,0 6' Mu his ATTORNEYS March 9, 1971 F. c. STUCKY 3,568,380

PREFABRICATED BUILDINGS Filed NOV. 5, 1968 7 Sheets-Sheet 2 [NV/5N! ()R.

FRITZ CHRISTOPH STUCKY %M@M.MM

his A TTORNEYS QMarch 9,1971 F. c.sTucKY I 3,563,380

PREFABRICATED BUILDINGS Filed Nov; 5. 1968 7 Sheets-Sheet 3 'r w TF'T- A INVENIOR. FRITZ ICHRISTOPH STUCKY BY 3 m k g 6%,M

his ATTORNEYS March 9,

Filed Nov.

F. C. STUCKY PREFABRICATED BUILDINGS 5, 1968 '7 Sheets-Sheet 4 ZZ'Z ZYZf-ZW ffffiii fifiiziifi F/G' INVEN'IOR FRITZ CHRISTOPH STUCKY W QM,M

& 2AM

his ATTORNEYS March 9, 1971 s c 3,568,380

PREFABRIGATED BU ILDING 8 Filed Nov. 5, 1968 7 Sheets-Sheet s 1PM? z'sd INVEN'I'OR. FRITZ CHRISTOPH STUCKY his ATTORNEYS March 9, 1971 F. c. STUCKY 3,568,380

PREFABRICATED BUILDINGS Filed Nov. 5, 1968 7 Sheets-Sheet v FIG. 23

FIG. 24

FIG. 25'

5 FIG. 26

INVli/V'I ()R.

FRITZ CH RISTOPH STUCKY FIG. 27 59 6M MM hlS ATTORNEYS United States Patent 3,568,380 PREFABRICATED BUILDINGS Fritz C. Stucky, Zug, Switzerland, assignor to Elcon A.G.

Filed Nov. 5, 1968, Ser. No. 773,460 Claims priority, application Great Britain, Nov. 10, 1967,

51,155/67; July 26, 1968, 35,710/68 Int. Cl. E04b 1/06; E0411 1/12, 9/06 US. Cl. 5279 17 Claims ABSTRACT OF THE DISCLOSURE A prefabricated building unit, for forming the structural framework or back-bone of a transportable prefabricated building unit, consists of a prefabricated rectangular floor panel structure having a prefabricated vertical load-bearing column rigidly attached to it at each corner and at an intermediate region in the length of each side. In a modification a column may be omitted at one corner, and/or from one side, and replaced by a temporary column. Room elements may therefore be constructed of a length hitherto impracticable because in situ, the room elements in each upper storey are supported at the inter.- mediate region by the intermediate columns of the lower room elements, thereby reducing the unsupported floor span. The floor panel structure may" be a single panel or two co-planar panels disposed end to end at the intermediate region. It may be stressed to prevent it sagging (during transport and erection of the room element) at the intermediate region; the stress may be relieved or reduced after the room element has been placed in situ.

SUMMARY OF THE INVENTION The invention relates to prefabricated buildings comprising transportable prefabricated roorn elements and their method of construction and is particularly concerned with plural storey buildings and primarily those having at least three storeys. The expression transportable room element is employed herein to define a transportable cell-like structure having two opposed sides and two opposed ends and comprising a floor, and a vertical load-bearing end structure rigidly connected to the floor at each of said ends, which room element is adapted to be mounted at one or more of its sides side-by-side with and/or, at least at one of its ends, end-to-end or end-to-side with a further such room element in building up a storey of a building from the succession of such elements; the expression end structure includes a complete end wall and also includes vertical load-bearing pillars or columns adapted to have fill-in panelling applied to, or formed integrally with, them. The expression fill-in panelling includes a wall and a door or window. Such room elements and buildings incorporating them form the subject of US. Pats. Nos. 3,416,273 and 3,377,755, to all of which reference may be made for further particulars of constructions to which the present invention is applicable.

The chief advantage of the system of building construction employing transportable prefabricated room elements as above defined is that the room elements can be prefabricated to an almost final stage of construction at the factory, then transported to the building site, and there erected into the building, thereby reducing to a minimum the amount of work needed to be carried out at the building site. In particular the room elements may be completely finished in the factory With the electrical, plumbing and heating installations, glazing, and interior finish, applied to them leaving only the assembly and connection of the services to be carried out at the building site.

According to US. Pat. No. 3,377,755 the method of erection of a storey of a building comprises the steps of (a) building at a factory remote from the building site, load-bearing structural units each of which units comprises a reinforced floor panel and a vertical load-bearing end structure of reinforced concrete at each of two opposed ends of the panel and each end structure having two upstanding load-bearing columns spaced apart by a distance sufficient to accommodate a door or window and which panel and end structures are initially separate, by rigidly connecting an end structure, in the region of the base of each of its columns, to each of the two opposed ends of the panel in such a manner that said unit is capable of resisting, without cross-bracing or additional reinforcement, the forces to which the resultant room element is subjected to during manufacture, subsequent transport to the building site, and erection into the building, including forces tending to alter the angle between the floor panel and either end structure, (b) completing these units, prior to transport to the building site, into substantially-finished room elements by applying such external walls, doors, windows, non-load-bearing internal partition walls, plumbing, and wiring, as may be required and, -(c) transporting these substantially-finished room elements to the building site and there erecting them into said storey. The method by which the three initially separate components of the structural units are secured to one another forms the subject matter of US. Pats. Nos. 3,460,380 and 3,473,273 (to each of which reference is to be made); the latter also includes a jig for use in this operation.

Hitherto when employing a prefabricated building unit or structural unit according to U.S. Pat. No. 3,460,308 the preferred end-to-end length of that unit was between 8 and 10 metres. It has been found that from the architectural aspect a 6 metre unit might be more desirable particularly for dwellings. However, this is uneconomical from many aspects.

On the other hand it has been found that it would be economically desirable to use an even longer unit than hitherto as this has strong bearing on the cost of production and transport per m. floor area. In certain cases, like schools, such a longer unit is also architecturally desirable. For various reasons it would not be economical to endeavour to achieve this result by simply using two room elements mounted end-to-end in view of the statutory limitation placed on loads carried by road transport in various countries. Neither would it be practicable simply to double the length of the floor panel, for in a plural storey building this would lead to an uneconomically long unsupported span between the two end structures of each room element.

The present invention therefore provides a prefabricated building unit for a room element as hereinbefore defined, comprising a floor panel structure having two opposed sides, two opposed ends, and four corners, and at least six vertical load-bearing columns which are initially separate from, and of which not less than four are rigidly and permanently fixed to said structure, the location of said columns being at the corners and at an intermediate region in the length of the sides. This building unit is intended to form the structural framework or back-bone of a prefabricated room element as hereinbefore defined. It overcomes the difliculties hereinbefore discussed.

It will be appreciated that in a building having a storey composed of room elements incorporating such units the load-bearing columns of the room elements of each storey provide support for any superimposed part of the building such for example, as the room elements of a further storey, it being intended that the columns of successive storeys shall be in vertical alignment.

The floor panel structure may be a single panel or may consist of two co-planar panels disposed end-to-end at said intermediate region. It may be of reinforced, or reinforced and pre-stressed, concrete or may be of composite steelconcrete construction. The columns are desirably of reinforced concrete also.

Owing to the increased length of the resultant room elements which is made possible by this invention, difiiculties may occur in the handling (e.g. lifting and transport) of a room element in so supporting the latter that the fioor panel structure does not sag (i.e. is not deflected downwards by an excessive amount) and the room element is not subjected to warping. One way of overcoming these difficulties is, according to an important feature of the invention, to provide the floor panel structure with stressing means which applies a force to said structure tending to urge the structure upwards at the intermediate region. This stressing means may be a post-tensioning means that is to say, it is applied to the floor panel structure after the latter has been formed. It is desirably released, relaxed, or removed after the room element has been placed in position in order to relieve the camber and to allow the room element to be supported at the intermediate region on an underlying support such as for example, the column of a room element in a storey below.

According to another important feature of the invention the columns at the corners project slightly in plan beyond the sides and ends of the floor panel structure. Thus it is the external faces and corners of these columns, and not the size of the fioor panel structure itself, which decide the plan size of the resultant room element. Moreover external non-load bearing wall structures can be applied to the outer faces of the columns so that these columns are within the external walls of the building and are not subject to the effects of temperature variations.

According to another important feature of the invention each column is connected at its base to the floor panel structure by a joint which comprises a plurality of metal elements projecting from one of the two members to be connected (i.e. the said structure and the column) and received in clearance holes in the other member, and an adhesive filling occupying the clearance in each hole and bonding said elements into their holes. Desirably, but not necessarily each column stands on the upper surface of the floor panel or structure. This is advantageous because it permits the positions of the columns to be readily adjusted in all directions (for example, with reference to some form of jig) before they are fixed to the floor panel structure so that the overall dimensions and angles of the structure and therefore of the resultant room element accurately comply with design requirements regardless of the inevitable manufacturing tolerances of the several components. As hereinafter appears it also permits a variation in the position of the intermediate column or each of them in the length of the unit.

This invention also includes a method of fabricating a structural unit for a room element, and a method of building construction.

In order that the invention may be better understood, reference will now be made to the accompanying drawings in which:

FIG. 1 is a perspective view showing one form of prefabricated building unit according to this invention;

FIGS. 2, 3 and 4 are perspective views showing various arrangements of the columns;

FIG. 5 is a perspective view showing the use of a temporary removable column;

FIG. 6 is a perspective View of another form of unit according to this invention;

FIG. 7 is an exploded sectional view showing the connection between the base of a column and the floor panel structure and illustrating the upper end of a column;

FIG. 8 shows how the columns of successive storeys sit on one another;

FIGS. 9 and 10 are sectional plan views showing the positions of the'columns in relation to the floor panel structure;

FIGS. 11 and 12 are respectively a side elevation and an underneath view illustrating diagrammatically a stressing means;

FIGS. 13 and 14 are diagrams illustrating how the stressing means can be released;

FIGS. 15 and 16 are respectively an elevation and a plan showing diagrammatically the removal of post-stressing cables;

FIGS. 17 and 18 are detailed views showing the anchorage for one end of a post-stressing cable;

FIG. 19 is a sectional elevation showing a releasable connection between two such cables while FIGS. 20, 21 and 22 are respectively a sectional view through this connection, a plan view thereof, and an end view;

FIG. 23 is a diagram illustrating the loads composed during transport;

FIG. 24 is a pre-stressing moment diagram;

FIG. 25 is a further moment diagram;

FIG. 26 shows the moments distribution when the room element is in position in the building but without the prestressing having been relaxed or removed;

FIG. 27 shows the moments distribution when the prestressing has been removed.

The structural unit illustrated in FIG. 1 comprises a floor panel structure 10 of rectangular form in plan view and having two opposed long sides 10a, 10b, two opposed ends 10c, 10d, and four corners. At each corner the unit is provided with a vertical load-bearing column 11a, 11b, 110, or 110, while at an intermediate location in the length of each side 10a, 10b there is an intermediate vertical loadbearing column He, or 11 These columns are of identical form. The overall length of the unit may be 12 metres (or of that order) its width in the order of 2.4 to 3 metres and its height about 3 metres. Desirably, the over-all length of the resultant room element is a multiple of the over-all width of the element. For example, the room element may be four times as long as it is wide.

The columns of any of the pairs may be connected at their upper ends by a cross member or lintel 11g as illustrated in FIG. 2 with reference to columns 11a, 11b. Alternatively the columns may be entirely separate as illustrated in FIG. 3.

In FIGS. 1 to 3 the columns are spaced apart for the full width of the unit. The minimum requirement is that they shall be spaced apart by a distance sufiicient to accommodate a door or window. This is illustrated in FIG. 4 in which a door opening 12 is provided between the two columns. This figure also illustrates the fact that one of the columns may be substantially wider than the other.

While it is necessary to have two corner columns at one end of the unit there may be less than two corner columns at the other end or less than two columns at the intermediate region. However, Where a corner or a side is void of a permanent column there may be provided a temporary removable column such as is illustrated at 13 in FIG. 5. This temporary column 13 fulfills all the loadbearing functions of a permanent column until the resulting room elements have been built into a building and some form of permanent support provided in its place (as for example by structurally connecting the floor panel structures, and/or ceiling of adjacent room elements) whereupon each such temporary column is removed.

FIG. 6 illustrates an alternative form of unit in which the floor panel structure 10 consists of two co-planar panels a, 1001). Each pair of columns 111a, and 111b, 111s and 111 and 1110 and 111d form integral parts of load-bearing structures 14, 15, and 16 in which their upper ends are connected by cross members or lintels 14a, 15a, 16a. The lower ends of the columns of the intermediate structure 15 are also connected by a cross member 1517. As illustrated in end structure 14 the space between the two columns may be wholly or partly filled by a fill-in panelling 116 (such for example as a Wall-forming panel) which may, if desired, be formed integrally with the columns.

It will be seen that structure 14 is applied to one end of panel 100a, structure 16 is applied to the opposite end of panel 11% while structure 15 is applied to the adjacent ends of these two panels which are arranged in the same plane. These various components are permanently and rigidly connected together at the region at the base of each column as described in US. Pat. No. 3,460,308.

The panel structure 10 of FIG. 1, and each panel 100a, 100b, of FIG. 6, may be made of reinforced, or reinforced and pre-stressed, concrete in which case it is suitably ribbed at its underside (see FIG. for strength and lightness. The columns 11a, 11d of FIG. 1, and the structures 14, 15, and 16 of FIG. 6 may be made of reinforced concrete.

FIGS. 7 and 9 show how the columns of FIG. 1 are connected to the panel structure by an adaptation of the joint described in US Pat. No. 3,460,308.

At each location where it is required to mount a column the panel 10 is provided with four clearance holes 17. At the lower end of each column its reinforcement rods 18 protrude as shown at 19, and are received in the clearance holes 17, and adhesive filling 20 is introduced into each clearance hole to bond each projecting element 19 to the floor panel structure. The adhesive filling may be a quick setting cement consisting of an epoxy resin mixed in the proportions of one to one by weight with quartz sand as an aggregate.

The fact that the holes 17 are clearance holes permits the columns to be accurately disposed in the required positions and at the required angles so that the unit has the required dimensional and angular accuracy without regard to the dimensional tolerances of its components. Thus FIG. 9 illustrates the fact that the column 11a, may have the same position regardless of manufacturing variations in the size of the panel structure 10 and the location of the clearance holes. Thus whereas a side and end of one panel structure are indicated in full lines at 10a, 10a and the holes at 17, the corresponding side and end of a panel structure of slightly dilferent size are indicated at 10'a and 10'c, and the position of the holes indicated therein at 17'.

FIG. 9 also shows that in plan the outer faces of each column may protrude beyond the margins of the panel structure. It may here be pointed out that this feature is also applicable to the unit shown in FIG. 6.

It will be appreciaed of course that the joint described with reference to FIGS. 7 and 9 as applied to a corner column is also employed for each intermediate column, and when so employed affords the same facility for accurate adjustment of the position and angle of the intermediate column. v

FIG. 1 illustrates additional series of holes 17 in the floor panel structure 10 whereby the panel 10 affords a choice among a plurality of holes 17 for fixing each column 11s and 11 in any selected one of a plurality of alternate positions.

FIG. 10 illustrates in plan the effect which is obtained when two room elements, the structural units of which have the same overall dimensions but the panel structures 10 of which vary in size within the manufacturing tolerances which are likely to be experienced, are mounted side by side. It will be seen that the exposed side faces of the columns 11a, 11b are in contact, or substantially so, at a vertical joint face 21 and the column faces that are presented at the end of the units occupy one and the same plane whereas the sides 100 of the two panels are not aligned. Furthermore, the spacing between the plane of the joint 21 and the end faces 10a, 10b of the panels is unequal.

Since the position and attitude of the columns is accurately defined it is possible to stack the room elements one on top of another with their columns in accurate and vertical alignment. This is illustrated in FIG. 8 which shows a part of the floor panel structure and the lower end of one column 11a of a room element in one storey and the upper end of the corresponding column of a room element of the storey below it.

It will be understood that not only are there manufacturing variations in the size and shape of the floor panel structures but there are inevitably manufacturing variations in the length of the columns. Yet it ;is necessary to achieve a high degree of accuracy between the plane occupied by the lower effective face of the floor panel structure (and conveniently defined by the lower faces of metal bearing pads 23 which are cast in position) and the plane occupied by the top ends of all the columns. Heightwise accuracy may be wholly or in part achieved by the introduction of the layer 22 of the setting cement between the lower end of each column and the upper surface of the floor panel structure. Alternatvely or in addition it may be wholly or partly achieved by applying to the top of each column a metal bearing plate 24 with a layer 25 of the quick setting cement between its undersurface and the top of the column. It will be understood that before the layer 25 has set the plate 24 may be forced downwards to give the unit the required overall height. Plate 24 is desirably firmly fixed to the column by joints consisting of protruding pins 27 bonded into clearance holes 28 in the column by a quick setting cement or adhesive.

In placing the room elements of an upper storey on top of the room elements of a lower storey it is desirable to locate pads 29 on top of the plates 24. These pads 29 may be slightly compressible.

:FIGS. 7 and 8 also illustrate the fact that the external wall panels 30 of the room elements are located against the outer faces of the columns. These panels 30 desirably comprise an outer skin 31, an inner skin 32, and a heat insulating layer .33 between them. The joint between the upper edges of the external wall panels of the room elements of one storey and the lower edges of the corresponding wall panels of the room elements of the next upper storey may be made by a compressible bead 34.

After the initially-separate components of the unit have been permanently and rigidly connected together, and either before or preferably after the unit has been completed into a substantially finished room element by applying such external walls, door, window, non-load-bearing partition walls, plumbing, and wiring, as may be required, the floor panel structure is so stressed as to prevent it sagging (during transport and erection of the room elements) at the intermediate region occupied by the intermediate column or columns: i.e. at the transverse region occupied by the intermediate columns 11e, 11 in 'FIG. 1 or by the intermediate structure 15 in FIG. 6. This may be effected by pre-stressing cables 35 or the like which extend in ribs at the underside of the floor panel structure. The stress is relieved or reduced after the room element has been placed in position. This may be effected by cutting the cables or releasing their anchorages. However, it may still be desired to ensure that each length of the floor panel structure at opposite sides of the intermediate region remains pre-stressed against sagging. Thus referring to FIG. 13 at opposite sides of the region there are recesses or grooves 36, 37 whereat the cables are exposed. Between recess 36 and the left end of the floor panel structure and between recess 37 and the other end thereof the cables are bonded into the said structure, but between said recesses the cables are not bonded. Thus when the cables are cut in the recess 36 or 37 the stress tending to resist sagging of the region is released but each part of the floor panel structure to the left and right remains pre-stressed.

Cutting all the cables simultaneously in this manner would result in a sudden release of the pre-stressing force. This may be avoided by providing sets of individual wires 35a, 35b in FIG. 14, in which case either the individual wires are all cut one after the other so that the stress released is effected in stages, or in the alternative only one set of cables is cut leaving the other set intact so that the pre-stressing force is merely reduced.

It may be desired to recover the cables, intact, for re-use. In this event they are not bonded into the floor panel structure but extend freely through conduits therein so that, as illustrated in FIGS. and 16, after the anchorages 38 at one end of each cable have been released that cable may be drawn out of its conduit from the other end. The anchorages 38 are disposed at the top surface of the floor panel structure and within the exterior confines of the room elements so that the cables can be drawn out of the erected room elements without it being necessary to provide the building with exterior staging or platforms to support the workmen effecting the withdrawal. I

It may be desirable to curve the ends of the cables hori zontally inwards so as to remove their anchorage points from the most likely vicinity of parts, such as partition walls, which might obstruct access to them or prevent the cables being withdrawn; this is illustrated in FIG. 17.

FIG. 18 illustrates one of the end anchorages. It will be seen that the cable extends through a conduit 39 in the floor panel structure and is gripped between the two halves 40 of a tapered split collet which is itself engaged in a tapered sleeve 41 cast into the floor panel structure. These collets may be loosened and extracted in a conventional manner in order to be able to relax or remove the cable.

Instead of releasing the pre-stressing force by cutting the cable it may be released by disconnecting the cable at its centre. This is illustrated in FIGS. 19 to 22. Each cable consists of two portions 35c, 35d which are connected within a pocket 42 within the intermediate region by a releasable coupling 43. Cable portion 35c is bonded into the panel structure 10 except for one end which prO- trudes into pocket 42. Cable portion 35d is likewise bonded into the panel 10 except at or in the neighbourhood of the aforesaid region where it extends through a clearance duct 44 with an end protruding into the pocket 42. The protruding cable ends are gripped by split tapered collets 46 which are themselves received in tapered seat in the interior of the body of the coupling 43. This body 45 consists of two halves 45a, 45b which are normally held closed together but which may be moved apart as illustrated in FIG. 22 to release the split collets 46.

It will be appreciated that in the room element according to the invention the floor panel structure is designed to withstand the loads as they occur in the building after erection, where the panel is fully supported in the intermediate region. Hence, if the panel structure itself has a span during transport of 12 metres, it will in fact have 2 spans of only, say, 6 metres between supports after erection. This makes it possible to design a light panel structure not requiring pre-stressing over a span of only, say, 6 metres. However, FIG. 23 illustrates that the moments due to imposed load during transport (i.e. without support at the intermediate region) are in excess of the design capacity of the light structure (indicated as two dotted lines in FIG. 23).

In order to hold the bending stresses caused by the moments within the capacity of the structure the latter is pre-stressed in the manner described and in accordance with the moment diagram of FIG. 24. The resultant of the moments imposed by the load and induced by the prestressing is illustrated in FIG. 25. It shows that the resultant stresses are now within the capacity of the structure.

If this room element with the pre-stressed panel structure is now placed in position in the building, i.e. supported at the intermediate region, the resultant stress reversal in this region produces a distribution of moments according to FIG. 26. This shows that the moments in this region exceed the capacity of the structure.

In order to rectify this the pre-stressing has either to be relaxed in the intermediate region over a width corre- 8 sponding at least to the distance X in FIG. 26, or to be removed entirely throughout the length of the panel, in the manner described above.

If the pro-stressing is removed completely the distribution of moments would correspond to FIG. 27 which is the state for which it had been designed, assuming full support at the ends and at the intermediate region of the floor panel structure.

It is further to be understood that the structural units are fabricated from the prefabricated components at a factory remote from the building site at which the building is to be erected. Also at this factory the structural units are completed intosubstantially finished room elements by applying such external walls, doors, windows, non-load-bearing internal partition walls, plumbing, and wiring, as may be required in such room elements. The substantially finished room elements are then transported to the building site and there erected into a-building.

The roof or ceiling of the room element is not shown in the accompanying drawings. It is preferably a horizontal substructure comprising horizontal members which extend between the upper ends of adjacent columns and which can be used to brace the upper ends of the columns and thereby to add stiffness to the structural unit and to the room element.

There are two preferred methods of erecting room element buildings according to the invention.

In the first method conduits for accommodating prestressing cables or wires are incorporated in the floor panel in the course of its prefabrication, e.g. pre-casting in concrete. The pre-stressing is applied substantially at the end of the assembly line manufacturing the room elements. This has the advantage that the shape of the floor plate is virtually identical to that it takes after erection, so that closer tolerances may be kept in the internal fitting out of the room elements at the factory. The pre-stressed room element is transported to the site in the usual manner, i.e. with end support for the floor panel. It may also be lifted and positioned in the building in the usual manner, i.e. by lifting it at the four corners. After positioning the prestressing is completely relaxed, and the cables preferably removed.

In the second method the pre-stressing is applied as described, to the floor panel during the process of prefabrication. The processes of transport, manufacture, and lifting proceed, as usual, ie as for much shorter room elements in which the whole vertical load can be supported on the four corners of the element without over-stressing the floor panel structure. After positioning the element the prestressing is relaxed, as described, a least in the intermediate region.

What I claim is:

1. A prefabricated building unit comprising a transportable cell-like structure comprising a horizontal prefabricated floor panel having two opposed sides, two opposed ends, and four corners, and at least four prefabricated vertical load-bearing column members rigidly and permanently afiixed to the floor panel, three of the four column members being located at one corner of each end and at an itnermediate position along one side, respectively, and the fourth being positioned at a position along one side corresponding to the position of one of the first three column members along the opposite side.

2. A prefabricated building unit in accordance with claim 1 wherein the floor panel comprises a single panel.

3. A prefabricated building unit in accordance with claim 1 wherein the floor panel comprises two co-planar panel members having adjacent ends joined at the intermediate region.

4. A prefabricated building unit in accordance with claim 1 wherein the floor panel is formed with a plurality of clearance holes at the position of at least one column member and including a plurality of metal elements projecting into corresponding clearance holes, the columns being rigidly and permanently attached to the floor panel by bonding of the metal elements in the clearance holes.

5. A prefabricated building unit in accordance with claim 4 wherein the intermediate region on the floor panel is formed with at least two adjacent pluralities of clearance holes for receiving the projecting metal elements of a column member at alternate locations on the floor panel.

6. A prefabricated building unit in accordance with claim 4 wherein the clearance holes are substantially larger than the metal elements, permitting accurate positioning of the column member prior to bonding.

7. A prefabricated building unit in accordance with claim 1 wherein floor panel and the column members comprise reinforced concrete.

8. A prefabricated building unit in accordance with claim 1 including stressing means for applying stress to the floor panel to urge the intermediate region thereof upwardly.

9. A prefabricated building unit in accordance with claim 8 including stress control means for controlling the stress applied by stressing means.

10. A prefabricated building unit in accordance with claim 9 wherein the stressing means comprises cable means and the stress control means comprises cable releasing means.

11. A prefabricated building unit in accordance with claim 10 wherein the cable releasing means comprises means permitting separation of the cable means at a selected location in the floor panel.

12. A prefabricated transportable room element structure comprising a horizontal floor panel having two opposed sides, two opposed ends, and four corners, and a plurality of vertical column members rigidly and permanently affixed at corners of the floor panel, the columns being positioned so that at least one vertical face thereof protrludes beyond the corresponding edge of the floor pane 13. A prefabricated transportable room element structure in accordance with claim 12 including at least one column member rigidly and permanently afiixed to the floor panel along one side in a region intermediate the ends of the floor panel and having a vertical face which protrudes beyond the edge of the floor panel.

14. A method of prefabricating a transportable cell-like structure unit for use as a room element, the structure including a floor panel having two opposed sides, two op posed ends and four corners and at least four vertical loadbearing columns of substantially room height, each column having a base, comprising (a) positioning a column at each corner of one end of the floor panel,

(b) positioning a column at at least one corner of the opposite end of the floor panel,

(0) positioning a column at an intermediate region along one side of the floor panel, and

(d) fastening the base of each column permanently and rigidly to the floor panel.

15. A method in accordance with claim 14 further comprising the step of stressing the floor panel with an adjustable stressing means so as to urge the intermediate region thereof upwardly.

16. A method in accordance with claim 14 including the step of positioning at least one of the columns so as to project laterally beyond the floor panel.

17. A method in accordance with claim 14 including the step of adjusting the vertical height of at least one column prior to fastening it to the floor panel.

References Cited UNITED STATES PATENTS 1,618,886 2/1927 Peterson 52295X 3,015,912 1/1962 Fistedis 52223X 3,378,971 4/1968 Singer et al 52236X 3,442,056 5/1969 Van der Lely et al. 5279 3,460,308 8/1969 Stucky et al 5279X FOREIGN PATENTS 1,157,412 5/1958 France 5279 1,062,785 3/1967 Great Britain 52745 PRICE C. FAW, JR., Primary Examiner US. Cl. X.R. 52223, 295, 745 

